Genetic variation and zoogeography of pine voles of the Microtus subterraneus/majori group in Europe and Asia Minor

Karyotypic and allozyme analyses were carried out on 55 individuals of Micr otus subterraneus and M. majori from 19 populations in Europe and Anatolia. The occurrence of M. subterraneus in Asia Minor was proven. Standard karyo types were found in M. majori (2n = 54), M. subterraneus from Poland (2n = 54), and central and south-eastern Europe (2n = 52). Although the karyotype of M. subterraneus populations from Anatolia (2n = 54), resembled that fro m Poland, there were apparent differences in the X chromosomes: it was larg er and submetacentric (instead of metacentric) in the Anatolian populations owing to the presence of a large block of heterochromatin. The heterochrom atic segment was also found to cause the size and shape differences in the X chromosomes between M. majori and European.11. subterraneus (both in the 2n = 52 and 2n = 54 karyotypes). However, the location of this segment diff ered between the latter species and M. subterraneus from Anatolia. The dist ribution of the 2n = 52 and both the 2n = 54 karyotypes of M. subterraneus suggests that the Robertsonian fusion, distinguishing these different karyo types, originated within the range of the species (i.e. within the 54-chrom osome karyotype) and has spread subsequently towards its periphery. It is a lso suggested that both the fusion in European populations and amplificatio n of heterochromatin in Anatolian populations are quite recent phenomena. T he allozyme data indicate that gene flow is limited between populations of M. subterraneus and they are concordant with the isolation-by-distance mode l. There seems to be little correspondence between patterns of chromosomal and allozyme variation in M. subterraneus. Nei's genetic distance between M . subterraneus and M. majori was low (D = 0.169), suggesting their recent d ivergence.